Are you calculating the bpm as the distance they travel or their resulting speed at that many strokes?

I calculated the time it would take for the tip of the stick to accelerate from rest to 3e8 m/s over a distance of 10 cm. First you calculate the average acceleration, then the time. That's the time it'll take for the down stroke; the upstroke will take the same amount of time as the downstroke. Each stick does 2 upstrokes and 2 downstrokes per beat of sixteenths, so you can figure out how long each beat will be in seconds. You can work it out from there to get beats per minute.